1 !' 1 ^ 1 Hall-Good speed : Ch rysil 253 



scale. Whether or not Chrijsothcuiinus eould be "improved"' to the 

 same extent is a question which we are unable to answer, for the two 

 plants are so different in their life histories that methods used success- 

 fully with one might entirely' fail with the other. Nevertheless it seems 

 logical that the possibilities of both should be tested out before either 

 one is exclusively selected for cultivation, since each possesses certain 

 advantages which the other does not have. It is in order to draw a 

 comparision between the two that the history of the introduction of 

 Guayule into cultivation has been briefly outlined above. 



The great superiority of Guayule lies in its high rubber content. 

 As stated above, this averages ten per cent for wild plants as against 

 an average of only 2.5 per cent for the I'iriduhis form of Chrysotham- 

 niis. These figures are based upon pure dry rubber and dry shrub. 

 Guayule; moreover, has been extensively studied : its habits, and its 

 response to treatment, are at least somewhat understood, and the work 

 thus far done upon it has resulted in the development of a fifteen to 

 seventeen per cent strain. Tlie improvement of Chrijsofhamnus could 

 undoubtedly be brought about, at least to some extent, by selection 

 and ])reeding. However, since it is presunmbl>' a cross fertilized 

 plant, the separation of .superior strains would be a more difficult mat- 

 ter than in Guayule. A starting point is indicated in that certain in- 

 dividuals of the variety consimiUs actually ran as high as 6.7 per cent. 



Guayule has a still further advantage in that the methods of field 

 management, of milling, and of marketing are also established and the 

 product is well known to the rubber trade. Here, however, the ad- 

 vantages of Guayule over ChrijsotJiamnHs seem to end. 



As an offset against the above more favorable attributes of Guayule. 

 and especially the higher rubber content, we find a number of points in 

 favor of Chrysothdnuius. These are here set down in order that the 

 ^Mexican plant may be used to some extent as a gauge in measuring the 

 possibilities of tlie other one. 



(1) Chrysofhdiiiiius is a larger plant than Guayule, tlie wild shrubs 

 averaging six {)ounds of rubber carrying wood, whereas the plants of 

 the latter weigli one-half to three ]iounds, rarely attaining to six 

 pounds. 



(2j Chrysutliaiinius is a native of the western I'liited States and 

 is therefore adapted to our conditions. It grows where the tempera- 

 ture falls to zero and probably much lower, since it ranges up the 

 mountains to over 7000 feet altitude. In the consimilis form it is 

 known to grow over large areas where the temperature not infrequently 



